1. Field of the Invention
This invention relates to an ignition control device and an ignition control method for an internal combustion engine, with which to ignite a combustible air-fuel mixture in a combustion chamber of the internal combustion engine.
2. Description of the Related Art
In recent years, problems relating to environmental degradation and fuel depletion have become more serious, and addressing these problems has become an urgent task in many industries, including the automobile industry. In one technique proposed in response to these problems, a dramatic improvement in fuel efficiency is achieved by reducing pumping loss through the use of exhaust gas recirculation (EGR).
However, burned gas discharged as exhaust gas is noncombustible and has a larger heat capacity than air. Therefore, when a large amount of burned gas is taken back into the combustion chamber by EGR, the ignitability and combustibility of the combustible air-fuel mixture deteriorate.
In an ignition device for an internal combustion engine proposed as a solution to this problem, a spark discharge is maintained for a longer period using two pairs of coils so that the ignitability of the combustible air-fuel mixture can be stabilized and a stable flame kernel can be formed, and as a result, the combustibility of the combustible air-fuel mixture can be stabilized (see Japanese Patent Application Publication No. 2015-129465, for example).
In this ignition device for an internal combustion engine, first and second ignition signals are generated such that a first discharge period extending from the start to the end of a discharge generated by energizing a first primary coil partially overlaps a second discharge period extending from the start to the end of a discharge generated by energizing a second primary coil, a start timing of the first discharge period is prior to a start timing of the second discharge period, and an overlapping discharge period between the first and second discharge periods corresponds to a set overlap period.
Further, the set overlap period is set in accordance with the first discharge period, a blow-out threshold serving as a minimum value of a discharge current value at which blow-out does not occur, and a minimum peak value serving as the discharge current value at the start timing of the first discharge period so that a peak discharge current is minimized within a range in which blow-out does not occur.
According to this ignition device for an internal combustion engine, by maintaining the spark discharge for a longer period so that the ignitability and combustibility of the combustible air-fuel mixture are stabilized, a large amount of burned gas can be introduced into the combustion chamber by EGR, thereby reducing the pumping loss, and as a result, an improvement in fuel efficiency can be expected.